U.S. patent number 5,113,027 [Application Number 07/533,513] was granted by the patent office on 1992-05-12 for oxychlorination process using a catalyst which comprises copper chloride supported on rare-earth modified alumina.
This patent grant is currently assigned to Vulcan Materials Company. Invention is credited to William Q. Beard, Jr., Robert P. Hirschmann, Barry M. Little, Eric L. Mainz, Earl B. Smith.
United States Patent |
5,113,027 |
Mainz , et al. |
May 12, 1992 |
Oxychlorination process using a catalyst which comprises copper
chloride supported on rare-earth modified alumina
Abstract
A superior catalyst for the oxychlorination of C.sub.2
hydrocarbon feeds comprises a mixture of copper chloride and alkali
metal chloride, especially potassium chloride, and preferably also
magnesium chloride, which mixture is deposited on an alumina
support that has been thermally stabilized by integral
incorporation therein of a certain class of lanthanide oxide. The
use of such thermally stable catalyst in the production of
chlorinated hydrocarbons such as trichloroethylene and
perchloroethylene by oxychlorination of a C.sub.2 hydrocarbon feed
results in particularly good process efficiencies in terms of long
on-stream times, relatively low reactor corrosion rates, high HCl
conversion, reduced burning, and conveniently flexible selectivity
to specifically desired product.
Inventors: |
Mainz; Eric L. (Colwich,
KS), Beard, Jr.; William Q. (Wichita, KS), Hirschmann;
Robert P. (Wichita, KS), Little; Barry M. (Castlewood,
SD), Smith; Earl B. (Newton, KS) |
Assignee: |
Vulcan Materials Company
(Wichita, KS)
|
Family
ID: |
27036320 |
Appl.
No.: |
07/533,513 |
Filed: |
June 5, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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451303 |
Dec 15, 1989 |
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Current U.S.
Class: |
570/224 |
Current CPC
Class: |
C07C
17/15 (20130101); C07C 17/158 (20130101); C07C
17/158 (20130101); C07C 21/10 (20130101); C07C
17/158 (20130101); C07C 21/12 (20130101) |
Current International
Class: |
C07C
17/00 (20060101); C07C 17/15 (20060101); C07C
17/158 (20060101); C07C 017/152 (); C07C
017/151 () |
Field of
Search: |
;570/224 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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701913 |
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Jan 1965 |
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CA |
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1256074 |
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Dec 1971 |
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GB |
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Other References
Abstract: CA:72:31207p (1970) corresponds to British Pat. No.
1,256,074. .
Abstract: CA 72:31208b (1970) corresponds to German Publ. No.
1,917,041. .
Abstract: CA 72:71145y (1970) corresponds to German Publ. No.
1,920,685. .
Abstract: CA 78:71395d (1973) corresponds to German Publ. No.
2,226,657. .
Abstract: CA 78:75562d (1973) corresponds to German Publ. No.
2,228,452. .
Abstract: CA 105:103451 (1986) corresponds to European Publ. No. EP
184,506. .
Abstract: CA 83:78548t (1975) corresponds to Spanish Pat. No.
396,465. .
Abstract: CA 83:78549u (1975) corresponds to Spanish Pat. No.
496,467. .
Abstract: CA 105:103446r (1986) corresponds to JP 6135851 (86
35,851). .
Abstract: CA 105:103447s (1986) corresponds to JP 6138627 (85
38,627). .
Abstract: CA 98:106780t (1983) corresponds to Braz. PI BR 82
00,180..
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Primary Examiner: Mars; Howard T.
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Parent Case Text
BACKGROUND OF THE INVENTION
1. Cross-Reference to Related Application
This application is a continuation-in-part of parent application
Ser. No. 07/451,303 filed Dec. 15, 1989. The entire contents of
said parent application are hereby incorporated herein by
reference.
Claims
What is claimed is:
1. In a process for the production of at least one chlorinated
hydrocarbon product selected from the group consisting of
trichloroethylene and perchloroethylene by catalytic
oxychlorination of a feedstock comprising a C.sub.2 Hydrocarbon
containing at least one less chlorine atom than the desired
product, the catalytic oxychlorination being conducted in contact
with a fluidized bed of particles of a copper chloride-containing
catalyst composition in a reaction zone maintained at a temperature
between 250.degree. and 470.degree. C. and at a pressure between 1
and 10 atmospheres, the improvement which comprises using as the
catalyst a composition comprising copper chloride and alkali metal
chloride deposited in catalytically active amounts on
microspheroidal particles of a support which has a surface area in
excess of 20 and less than 100 m.sup.2 /g and comprises at least
90% alumina having from 0.2 to 10% of a Lanthanide Oxide selected
from the group consisting of the oxides of lanthanum, enodymium,
praseodymium and yttrium and mixtures comprising at least two of
said Lanthanide oxides, intrinsically incorporated therein by heat
treatment of the alumina at a temperature of at least 800.degree.
C. and up to 1500.degree. C. after incorporation of a salt of the
Lanthanide in the alumina.
2. A process according to claim 1, wherein the alumina in the
support contains principally gamma-alumina, wherein the alkali
metal chloride is potassium chloride and wherein the ratio of
copper chloride to potassium chloride in the catalyst is between
0.8:1 and 5.0:1.
3. A process according to claim 1, wherein the reaction zone is
maintained at a temperature between 380.degree. and 450.degree. C.,
and the catalyst is present therein in the form of a fluidized bed
of microspheroidal particles.
4. In a process for the production of trichloroethylene and
perchloroethylene by catalytic oxychlorination of a feedstock
comprising a C.sub.2 Hydrocarbon containing at least one less
chlorine atom than the desired product, the catalytic
oxychlorination being conducted in contact with a fluidized bed of
particles of catalyst in a reaction zone maintained at a
temperature between 380.degree. C. and 450.degree. C. and at a
pressure between 1 and 10 atmospheres, the improvement which
comprises using as the catalyst a composition comprising copper
chloride and alkali metal chloride deposited in catalytically
active amounts on microspheroidal particles of an alumina support
which has a surface area between about 25 and 60 m2/g and which
contains at least 90% alumina and from 0.5 to 5.0 percent of a
Lanthanide Oxide selected from the group consisting of the oxides
of lanthanum, neodymium, praseodymium and yttrium and mixtures
comprising at least two of said Lanthanide Oxides, said Lanthanide
Oxide being intrinsically incorporated in said alumina support by
calcining said support at a temperature of at least 800.degree. C.
and up to 1500.degree. C. after impregnation with a salt of said
Lanthanide.
5. A process according to claim 4, wherein the Lanthanide Oxide in
the alumina support comprises the oxide of lanthanum which is
intrinsically incorporated in the alumina by calcining said support
at a temperature of about 1200.degree. C. after impregnation with a
salt of lanthanum.
6. A process according to claim 4, wherein the catalyst comprises
magnesium chloride in addition to copper chloride and potassium
chloride, said magnesium chloride being present in a ratio equal to
one weight of MgCl.sub.2 per between 0.5 and 3.0 weights of KCl.
Description
2. Field of the Invention
The invention relates to the production of perchloroethylene and
trichloroethylene by catalytic oxychlorination of C.sub.2
hydrocarbons or their partially chlorinated derivatives, to
catalyst compositions for use in such oxychlorination processes and
to modified alumina supports used in making such catalysts.
3. General Background and Summary of the Prior Art
Perchloroethylene, C.sub.2 Cl.sub.4, and trichloroethylene, C.sub.2
HCl.sub.3, are chlorinated hydrocarbons which are widely used as
solvents in dry cleaning textiles, in degreasing metal parts, in
various solvent extraction processes, in compounding rubber
cements, and in various other operations. Because perchloroethylene
is relatively stable, its use is much less severely restricted by
anti-pollution regulations than is the use of most other
chlorinated solvents and is therefore a particularly desirable
product. Trichloroethylene is becoming increasingly important as a
raw material for the manufacture of replacement refrigerants for
fully halogenated refrigerant compounds currently in use.
Both C.sub.2 Cl.sub.4 and C.sub.2 HCl.sub.3 have been commonly
produced by catalytic oxychlorination of ethane, ethylene or a
partially chlorinated derivative thereof, i.e., by reacting such a
feedstock with hydrogen chloride or chlorine and air or oxygen at a
suitable temperature in the presence of a suitable catalyst which
is maintained in the reaction zone either as a fixed bed or, more
preferably, as a fluidized bed.
Typically, such catalyst compositions comprise a catalytic amount
of a metal having a variable valence, such as copper, as well as an
alkali metal, such as potassium, supported on a suitable carrier.
Carriers used commercially in the past have included highly
calcined fuller's earth, such as "Florex", or preferably synthetic
activated aluminas. See, for instance, U.S. Pat. Nos. 3,267,162,
3,296,319 and 4,463,200. Fuller's earth is essentially a
magnesium-aluminum silicate containing small proportions of oxides
of iron, calcium, potassium and titanium. By contrast, synthetic
activated alumina consists essentially of alumina with virtually no
significant impurities or at the most only a very small proportion
of silica.
Researchers working on catalytic oxychlorination processes in the
past have in some instances expressed a preference for the use of
low-surface area alumina as catalyst supports, i.e., for supports
having a surface area below 10 m.sup.2 /g, and especially between 2
and 5 m.sup.2 /g, as in U.S. Pat. No. 4,124,534. In other instances
they have expressed a preference for high-surface area alumina as
catalyst supports, i.e., for supports having a surface area of at
least 100 m.sup.2 /g, as in U.S. Pat. No. 4,463,200. Low-surface
area supports have been recommended mainly because they were
thought to result in higher HCl conversions and lower carbon
burning; see, for instance, U.S. Pat. No. 3,427,359 and French
Patent No. 1,386,023. On the other hand, high-surface area supports
have been recommended because they were through to contribute to an
increased selectivity of the reaction toward the production of
perchloroethylene as the desired product and a reduced formation of
undesirable 1,1,2-trichloroethane and unsymmetrical
tetrachloroethane, as indicated in U.S. Pat. No. 4,463,200.
Catalysts comprising a low-surface area support have been found to
be relatively unstable in that such supports possess only a
relatively small number of binding sites for retaining the active
metal salts in the composition, and the resulting loss of the metal
salts from such catalysts has been found to constitute a
significant factor in causing corrosion of the metal reactors in
which such oxychlorination reactions are generally carried out. In
addition, especially when low-surface area supports such as
diatomaceous earth or other silica-aluminas are used, high
selectivities of perchlorethylene and trichloroethylene are only
obtained at very high temperatures.
Catalysts based on high-surface area supports, which have been used
successfully in producing ethylene dichloride at temperatures below
350.degree. C., retain their catalytic salts well but have been
found to cause substantial destruction of the feed material because
of its oxidation to form carbon oxides. This becomes especially
serious when unchlorinated ethane or ethylene or ethyl chloride is
used as the feed to make more highly chlorinated hydrocarbons such
as perchloroethylene and trichloroethylene, the production of which
requires reaction temperatures near or above 400.degree. C. in
order to obtain good selectivity. Conversely, poor selectivity to
the desired products has tended to occur when low-surface area
aluminas were used as catalyst supports. Moreover, such prior
catalyst compositions have been frequently found to have a
relatively limited useful life because they have only moderate
thermal stability and consequently tend to lose surface area and
become sticky and corrosive to metal reactor walls as the
oxychlorination process continues, especially at reaction
temperatures above 350.degree. C.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an improved
oxychlorination process for the production of perchloroethylene and
trichloroethylene, which process avoids or substantially alleviates
the disadvantages and problems of the prior art discussed
above.
A more particular object is to provide an oxychlorination process
for the production of perchloroethylene and trichloroethylene,
wherein physical stability of the catalyst support is improved and
corrosion of metal reactor surfaces is avoided or minimized.
Another object is to provide an improved, more stable catalyst for
use in the production of perchloroethylene and trichloroethylene by
oxychlorination, such that the disadvantages and problems
encountered in the prior art may be avoided or substantially
alleviated.
A corollary object is to provide an improved catalyst for the
production of perchloroethylene and trichloroethylene by
oxychlorination, which results in improved overall feed conversions
and reduced reactor corrosion.
Another particular object is to provide an improved,
microspheroidal alumina support for catalysts to be used in the
production of perchloroethylene and trichloroethylene by catalytic
oxychlorination, which alumina support possesses improved long-term
surface area stability and consequently results in catalyst
compositions which are operable over longer periods of time without
becoming sticky and corrosive due to salt overload such as occurs
when the surface area of the catalyst support becomes reduced in
the process.
Another object is to provide an improvement in the production of
perchloroethylene and trichloroethylene by oxychlorination of
ethane, ethylene or partially chlorinated derivatives thereof,
using a novel catalyst which gives improved performance in the form
of reduced carbon burning and usually also increased conversion of
hydrogen chloride or chlorine as well as higher total selectivity
to the desired products.
In essence, the present invention provides an improved catalyst
composition for the oxychlorination of C.sub.2 hydrocarbons or
partially chlorinated derivatives thereof at a temperature between
about 250.degree. and 470.degree. C. This composition comprises as
a support a rare-earth modified, substantially pure, high- to
intermediate-surface area activated alumina, i.e., an
activated-alumina containing only 0 to about 5 percent silica, most
preferably not more than 0.5 percent silica, and from 0.2 to 10
percent of a certain class of rare earth, i.e., an oxide of a
lanthanide other than cerium or an oxide of yttrium, that is, an
element having an atomic number of 39, 57 or 59 through 71,
preferably an oxide of neodymium or praseodymium, or most
preferably an oxide of lanthanum. The use of the oxide of cerium
(atomic no. 58) by itself is counterproductive but its admixture
with one or more of the desirable Lanthanides is permissible in
minor proportion, e.g., less than 50 percent, preferably less than
15 percent, based on the weight of the desirable Lanthanide Oxide
or Oxides. Cerium oxide is at best a diluent. All these suitable
lanthanide metals, including yttrium but excluding the ineffective
cerium, are for convenience referred to in this specification and
appended claims as "Lanthanides", and the corresponding oxides are
referred to as "Lanthanide Oxides."
The present invention employing the incorporation of such
Lanthanide Oxide as an integral part of the alumina support has
been found to result in alumina supports possessing a remarkably
improved thermal stability of their surface areas in
oxychlorination reactions. No such stabilization of alumina
supports is known to have been resorted to in the production of
oxychlorination catalysts, as no logical reason for doing so was
thought to exist since oxychlorination reactions are usually run at
temperatures much below the normal 1200.degree. C. transition
temperature at which gamma-alumina changes to the low-surface-area
alpha form. Thermal stabilization of alumina by incorporation of a
Lanthanide Oxide such as lanthana is, however, not broadly new and
has been employed in the manufacture of granula supports for
platinum catalysts used in automotive exhaust canisters.
Another aspect of the present invention involves an improvement in
the production of perchloroethylene and trichloroethylene by
high-temperature oxychlorination of at least one C.sub.2
hydrocarbon or a partially chlorinated derivative thereof, using as
a catalyst a copper chloride-alkali metal chloride mixture
deposited on a Lanthanide-modified alumina support and which
catalyst support has its surface area closely controlled within a
range that is in excess of 20 and less than 100 m.sup.2 /g. When
such a catalyst composition is to be used in a fluidized-bed
process, it is desirable that it be composed of microspheroidal
particles having an average particle size of between about 30 and
about 70 microns, as is otherwise well known. However, the present
invention is also applicable to the coarser-size catalyst
compositions customarily used in a fixed-bed oxychlorination
process, e.g., particles having an average diameter in the range of
from 1.0 to 10.0 mm.
Between about 10 and about 25 percent of the copper chloride-alkali
metal chloride catalyst mixture (based on the weight of the total
catalyst composition) is preferably loaded onto the novel support
the catalyst salt mixture possessing a copper chloride/alkali metal
chloride weight ratio of from 0.5:1 to 5.0:1, calculating the
copper chloride as CuCl.sub.2. Thus the use of the term "calculated
as CuCl.sub.2 " signifies in this specification and claims that
where cupric chloride (CuCl.sub.2) is employed in the catalyst
mixture, e.g., to obtain a copper chloride/alkali metal chloride
ratio of 1.2:1, 1.2 g cupric chloride is employed per gram of
potassium chloride. If cuprous chloride (CuCl) is employed instead
of CuCl.sub.2 in making a catalyst mixture having the same copper
chloride potassium chloride ratio of 1.2:1, just enough cuprous
chloride (0.9 g CuCl) must be employed so that 1.2 grams of reacted
cupric chloride will be present in the catalyst composition per
gram of potassium chloride upon conversion of the cuprous chloride
to cupric chloride in the oxychlorination reaction. Because
modification of the alumina supports by an oxide of a Lanthanide in
accordance with the present invention affords wide flexibility in
the selectivity of the oxychlorination process in producing either
more or less perchloroethylene relative to trichloroethylene, a
significantly wider range of copper chloride/alkali metal chloride
ratios is practical in the present invention than in the invention
disclosed in the parent application Ser. No. 07/451,303, identified
above.
A further improvement involves an oxychlorination catalyst which
comprises a magnesium compound, such as magnesium chloride,
magnesium nitrate or magnesium acetate as an additional component
of the CuCl.sub.2 -KCl catalyst mixture that is loaded on an
activated Lanthanide Oxide-modified alumina support. The desired
weight ratio of potassium chloride to magnesium chloride is from
0.5:1 to 3.0:1 and is most preferably between about 0.5:1 and about
2.0:1, irrespective of the surface area of the support.
The desirable ratio of copper chloride to the sum of potassium
chloride plus magnesium chloride in the catalytic salt mixture is
within the range of 0.5:1 to 2.0:1, most preferably between 0.5:1
and 1.5:1, the specific, optimum ratio being dependent on whether
trichloroethylene production is desired or is to be kept to a
minimum. Increasing the ratio of copper chloride to the sum of
potassium chloride plus magnesium chloride in the salt mixture to
1.5:1 or more favors lower trichloroethylene and higher
perchloroethylene selectivity, whereas decreasing the ratio of
copper chloride to the sum of potassium chloride plus magnesium
chloride to 0.5:1 or less favors increased trichloroethylene and
reduced perchloroethylene selectivity.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Perchloroethylene and trichloroethylene may be produced by
catalytically oxychlorinating a C.sub.2 hydrocarbon such as ethane,
or ethylene, or an incompletely chlorinated derivative thereof such
as ethyl chloride or ethylene dichloride (1,2-dichloroethane) or a
mixture comprising two or more of these compounds. Ethane, ethylene
and ethylene dichloride are particularly preferred feedstocks. As
used in this specification and in the appended claims, the term
"C.sub.2 Hydrocarbon" means and includes ethane, ethylene, and any
partially chlorinated derivative thereof. Of course, recycle
chlorocarbon streams from the process can be used as feed sources.
Because the production of perchloroethylene and trichloroethylene
by oxychlorination is a highly exothermic process, it is best
carried out using a solid catalyst in a fluidized bed which, unlike
a fixed bed, minimizes the formation of undesirable hot spots and
facilitates the removal of the heat of reaction by means of heat
exchangers, as is otherwise well known in the art. See for example,
M. Leva, "Fluidization", McGraw-Hill 1959, pp. 6, 208-209.
Such oxychlorination is desirably carried out at temperatures of
between about 250.degree. and about 470.degree. C., preferably
between 370.degree. and 450.degree. C., and most preferably between
about 400.degree. and 430.degree. C. Reaction pressure may be
atmospheric, subatmospheric or superatmospheric, but preferably is
maintained between about 1 and 20 atmospheres (absolute), more
preferably between about 1 and 6 atmospheres.
The oxychlorination reaction is generally conducted for a time
sufficient to maximize the production of perchloroethylene and
trichloroethylene based on carbon utilization, and preferably such
that a mole ratio of perchloroethylene to trichloroethylene in the
product is kept above about 5:1 when wishing mainly to produce
perchloroethylene, and is kept at about 1:1 when wishing to produce
trichloroethylene as a co-product. For example, the superficial
reaction zone residence time may be from several seconds to several
minutes, e.g., from about 2 to 60 seconds, preferably from about 10
seconds up to about 30 seconds.
Oxygen may be supplied for the reaction as pure oxygen gas or more
commonly as an oxygen-containing gas, e.g., air or oxygen-enriched
air. As is otherwise well known in the art, the ratio of total feed
of oxygen to total feed of C.sub.2 Hydrocarbon is a variable number
which depends upon the specific composition of the feed and other
process design factors. The oxychlorination reaction may be
conducted with an amount of oxygen that is at least equal to the
stoichiometric amount required to completely oxychlorinate the
organic feed to the ratio of trichloroethylene and
perchloroethylene desired while at the same time converting all
displaced hydrogen to water.
Typically the amount of oxygen supplied ranges between this
stoichiometric amount and up to about 200% in excess of this
amount, preferably from about 10 to about 50% in excess of
stoichiometric. For instance, when making perchloroethylene by
oxychlorinating ethylene, the reaction may be represented by the
equation
In such a case it is preferred to use from 2.2 to 3 moles of oxygen
per mole of ethylene feed.
Hydrogen chloride o chlorine or both are also supplied to the
reaction mixture in addition to the organic feed material and
oxygen. The ratio of total feed of chlorine and/or hydrogen
chloride to total feed of organic feedstock again is a variable
number which depends upon the specific composition of the feed and
other process design factors, as is well known in the art. The
oxychlorination reaction is typically conducted with an amount of
chlorine and/or hydrogen chloride adjusted to reflect the ratio of
trichloroethylene and perchloroethylene desired, that is, at least
equal to about 50% of the stoichiometric required to oxychlorinate
the organic starting material completely to perchloroethylene.
For example, when ethylene dichloride is being catalytically
oxychlorinated to perchloroethylene, it is preferred to conduct the
reaction at a temperature between about 400.degree. and 430.degree.
C. and maintain the mole ratio of hydrogen chloride to ethylene
dichloride above about 1.6, preferably from between about 1.6 to
about 1.9, while maintaining the molar ratio of oxygen to ethylene
dichloride between about 1.5 and 2.2.
Perchloroethylene and trichloroethylene may be recovered from the
reaction product stream by any suitable technique known in the art.
Thus, the effluent from the reactor may be passed through a cooler
and a condenser to a phase separator which collects the condensed
chlorohydrocarbons and hydrochloric acid. The chlorohydrocarbon
stream from the phase separator may then be neutralized, dried, and
sent to a fractional distillation system for purification and
recovery of perchloroethylene and trichloroethylene.
When producing ethylene dichloride from ethylene by
oxychlorination, commercial processes have commonly been conducted
at temperatures below 300.degree. C., i.e., at relatively low
temperatures, and have in the past employed copper
chloride-containing catalysts based on high-surface-area alumina.
Other such processes have used naturally occurring minerals for
catalyst supports. In any case, to be commercially useful,
catalysts used in oxychlorination processes must have long-term
surface area stability. Otherwise they become inoperable because of
stickiness from salt overload when the surface are of the support
shrinks excessively. Loss of surface area in alumina catalyst
supports usually occurs because of a phase change from the gamma
phase to the more dense alpha-alumina phase which has a very
low-surface area range.
In the more recent adaptation of the oxychlorination reaction to
the production of perchloroethylene and trichloroethylene,
temperatures of around 420.degree. C. have been favored, i.e.,
temperatures which are significantly higher than when making
ethylene dichloride but still well below 1200.degree. C., i.e. well
below temperatures that are generally considered necessary to
produce alpha-alumina from the gamma phase by heat alone..sup.1 The
transition of gamma to alpha-alumina has also been reportedly
achieved in the 375.degree. to 425.degree. C. range by hydrothermal
treatment, but only under high pressures of at least 10
atmospheres..sup.2 HCl has also been reported to cause the
transition from gamma to alpha-alumina at well below 1200.degree.
C., e.g., at 850.degree. C..sup.3 Based on such data, the logical
expectation has been that the stability of an alumina-based
catalyst at low pressures, e.g., less than seven atmospheres, would
be substantially as good in an oxychlorination process conducted at
between about 370.degree. and 470.degree. C. as it has been known
to be in oxychlorination processes conducted at or below
300.degree. C. However, this expectation has been found to be
misplaced.
The simultaneous presence of steam and HCl in an oxychlorination
process apparently can effect the transition from gamma to
alpha-alumina at even lower temperatures, since a large decrease in
surface area, from 73 m.sup.2 /g to a mere 9 m.sup.2 /g, has been
observed in a copper chloride-potassium chloride catalyst based on
a gamma-alumina support in only 288 hours under oxychlorination
conditions of 418.degree. C. and about 4 atmospheres pressure. Such
a thermochemical degradation of conventional oxychlorination
catalyst compositions at temperatures near or above 400.degree. C.
has therefore been thought to make the production of
perchloroethylene or triohloroethylene by oxychlorination
uneconomical with this type of catalyst.
As indicated earlier herein, the essence of the present invention
lies in providing a special, improved catalyst composition for such
high-temperature oxychlorination of C.sub.2 Hydrocarbons. This
composition comprises a copper chloride-alkali metal chloride
catalyst mixture deposited on a carrier or support which is
characterized by being composed essentially of Lanthanide
Oxide-modified alumina having a properly selected surface area. In
particularly preferred catalyst compositions the catalyst mixture
comprises not only copper chloride and potassium chloride, but also
a certain proportion of magnesium chloride.
In U.S. Pat. No. 4,463,200 it has been disclosed that in the
manufacture of perchloroethylene by oxychlorination the use of a
copper chloride-potassium chloride catalyst supported on an
activated alumina support having a surface area of at least 100
m.sup.2 /g and preferably between 150 and 250 m.sup.2 /g results in
a significant reduction in the formation of undesirable by-products
such as 1,1,2-trichloroethane or 1,1,1,2-tetrachloroethane and that
this kind of high-surface-area support simultaneously favors a high
molar ratio of perchloroethylene to trichloroethylene in the
product. However, while such catalyst compositions using a
high-surface-area support result in excellent chlorine utilization,
we have found them to promote excessive destruction of the organic
feed material by converting it to oxides of carbon especially so
when operating at conditions selected to produce a high carbon
selectivity to trichloroethylene. Because of this, we have found
supports advantageous not only in the practice of the invention
described and claimed in our parent application Ser. No.
07/451,303, but also in the invention described in the instant
application.
More particularly, as already indicated in the Summary Section of
this specification, it has now been discovered that an improved
catalyst for the manufacture of trichloroethylene and
perchloroethylene by oxychlorination in a fluidized bed can be
obtained by using as the catalyst support an activated, Lanthanide
Oxide-modified alumina possessing a surface area that is in excess
of 20 m.sup.2 /g and less than 100 m.sup.2 /g, preferably between
about 20 m.sup.2 /g and about 80 m.sup.2 /g, and most preferably
between about 25 and 60 m.sup.2 /g.
Still more specifically, it has now been found that catalysts based
on alumina supports can be significantly improved in terms of their
mechanical attrition resistance as well a their resistance to
thermochemical degradation in an oxychlorination process when a
minor proportion, ranging from 0.2 to 10%, and preferably 0.5 to
5.0% (calculated as oxide), of a salt o oxide of the group of
"Lanthanides" defined in the summary portion of this specification
is integrally or intrinsically incorporated in the alumina. This
can be accomplished, for example, by impregnation of the alumina
with a solution of the Lanthanide salt and by subsequent
calcination, or by co-precipitation of the alumina and the
Lanthanide Oxide from solution and subsequent calcination at a
temperature of at least 800.degree. C., preferably between
1000.degree. and 1500.degree. C., most preferably at about
1200.degree. C. When the Lanthanide Oxide is intrinsically
incorporated and distributed in the alumina the Lanthanide is
substantially insoluble and cannot be selectively removed by
extraction with water or by superficial abrasion of the catalyst
particles.
This kind of Lanthanide Oxide addition to the alumina at these
concentrations has been found to produce a most beneficial
improvement in the properties of the support without any adverse
side effect on the desired functioning of the oxychlorination
process. This has been found true not only under moderate
temperature conditions but also under high temperature conditions
such as those normally used in the production of perchloroethylene
and trichloroethylene by oxychlorination of C.sub.2 Hydrocarbons.
Catalyst compositions based on these particular Lanthanide-modified
alumina supports showed no noticeable loss of surface area in
oxychlorination runs as long as about 1000 hours, and exhibited
excellent resistance to attrition. By contrast, mere impregnation
of a Lanthanide salt on an alumina support will leave the
Lanthanide in a form that is susceptible to removal from the
alumina support or the final catalyst composition by superficial
attrition or by dissolution in water or other solvent and will not
result in a comparable improvement.
The aluminas used in preparing such catalyst supports are
preferably first activated by heating at a suitable elevated
temperature at which the alumina is dehydrated, as is otherwise
known in the art. For instance, such activation can be conducted at
about 400.degree. or higher, e.g., at 500.degree. or 600.degree. C.
However, unactivated aluminas can also be used.
Preparation of alumina-based catalyst supports is of course known
in the prior art. Suitable processes commonly used for the
preparation of alumina supports are described, for instance, in
Applied Industrial Catalysis, Volume 3: "Alumina for
Catalysts-Their Preparation and Properties" pp. 63-111. In
practicing the present invention, stable catalysts can be obtained
when a Lanthanide salt is integrally incorporated into the alumina
before spray-drying of the aqueous alumina gel or other forming
operation for the support, followed by calcination of the resulting
microspheres to the desired surface area. Acceptable results can
also be obtained by catalyst compositions prepared with alumina
supports in which the Lanthanide Oxide is integrally incorporated
by: (a) adding through aqueous or solvent impregnation of a
Lanthanide salt to the formed support before activation and then
calcining to the desired surface area, or (b) adding a Lanthanide
salt to the activated support and recalcining at a temperature
above 800.degree., e.g., in a range between about 1000.degree. and
1500.degree. C. In imparting stability to the alumina, these
methods of modified alumina preparation produce results that are
distinctly different from, and otherwise better than, merely
loading a Lanthanide salt on the finished support as part of the
catalyst formulation such as has heretofore been proposed in U.S.
Pat. No. 3,210,431.
Increased amounts of a suitable Lanthanide Oxide have been found to
lessen the rate of surface area shrinkage with respect to time.
Increased stability can thus be imparted by the inclusion of a
larger concentration of a suitable Lanthanide Oxide in the catalyst
support.
When a Lanthanide Oxide-modified alumina support having a surface
area in the range of from more than 20 to less than 100 m.sup.2 /g,
and most preferably between 25 and 60 m.sup.2 /g, is loaded with a
proper amount of a catalytic mixture of copper chloride and
potassium chloride and used as a catalyst in a fluidized state in
the manufacture of trichloroethylene and perchloroethylene by
oxychlorination, overall feed conversions are maintained at high
levels over extended run times along with a substantial and
unexpected reduction in metal corrosion rates. Good thermal
stability of the catalyst and the concomitant low corrosion rate
are of course greatly desired in large-scale industrial
oxychlorination reactors but have been difficult to achieve.
As already stated in the summary section of this specification, the
catalytic metal salts are loaded onto the supports possessing the
selected surface area at a concentration of 10 to 25 percent, with
the weight ratio of copper(II) chloride to potassium chloride in
the catalytic salt mixture being from 0.5:1 to 5.0:1.0.
The most suitable amount of the catalytic salts used for any
particular catalyst composition is dependent on the surface area of
the support. Supports having a surface area greater than 100
m.sup.2 /g can support up to 30 or 35 percent of the copper
chloride and potassium chloride salts without experiencing
fluidization problems. However, such relatively high catalyst
loadings have been found to cause the microspheroidal catalyst
particles to become sticky and difficult to maintain in the
fluidized condition if loaded onto a support having a surface area
of less than 100 m.sup.2 /g. Accordingly, for a catalyst support
having a surface area in the range preferred in the present
invention, i.e., in excess of about 20 but less than about 100
m.sup.2 /g, a total salt loading of between 10 and 25 percent based
on the weight of the finished catalyst composition is preferred. In
the most preferable range, i.e., with surface areas between about
25 and 60 m.sup.2 /g, a total salt loading of between 15 and less
than about 20 percent based on the weight of the finished catalyst
is best used. Of course, it is important in such a case for the
surface area of the catalyst support to remain relatively stable,
as the present invention makes possible.
When the oxychlorination reaction is carried out in a fluidized bed
of microspheroidal catalyst, the C.sub.2 Hydrocarbon as defined
above, chlorine and/or a chlorine-containing feed gas, and air or
oxygen, all enter a lower portion of the reaction zone at a
combined velocity above the minimum fluidization velocity of the
catalyst. Depending on which particular chlorocarbon is desired as
the principal product, the ratio of C.sub.2 Hydrocarbon feed and
chlorine-containing feed can be varied to control the degree of
chlorination, i.e., to achieve the desired
trichloroethylene/perchloroethylene split.
The invention will next be illustrated by several working
examples.
CATALYST AND LIFE TESTS
EXAMPLE 1
Preparation of Catalyst For Use In 15.2-cm Diameter Reactor
In preparing catalyst compositions representative of the prior art
for use in Runs I-1 and I-2 (TABLE I), a 42-kg quantity of a
commercial microspheroidal alumina support, designated as Harshaw
Al-1401-P and composed essentially of high-purity alumina without
any Lanthanide Oxide or salt, was placed, either as such or after
calcination to obtain a certain reduced surface area, in an
epoxy-coated steel tray capable of being heated with steam pipes
fastened beneath it. For use in Run I-3, 4.9 weight percent
Lanthanide Oxide was additionally integrally incorporated in the
alumina support by impregnation with a Lanthanide salt solution and
subsequent calcination. An aqueous solution of 10.7 kg of
copper(II) chloride dihydrate, 5.6 kg of potassium chloride and
20.1 kg of water was poured over the support and mixed in
thoroughly with a small rake. The catalyst composition was dried to
a uniform brown color with 8-atmosphere steam in the heating pipes
under the pan. Target loading for this catalyst was 15.0 and 10.0
weight percent copper and potassium chloride respectively as
calculated by the total weight of the anhydrous metal chlorides and
the alumina or modified-alumina support.
The actual catalyst compositions produced, the conditions used in
the runs in which they were tested as well as the results obtained
in these tests are shown in Table I, Runs I-1, I-2, I-3. A
description of the reactor and test conditions used in these tests
is given in Example 3 below.
As the results show, catalyst compositions used in Runs I-1 and I-2
which were prepared from high purity alumina, suffered major
reductions in surface area, i.e., they showed themselves to be
thermally quite unstable under the conditions of these tests. This
is in sharp contrast to the novel catalyst composition using the
Lanthanide Oxide-modified catalyst support described in Example and
tested in Run I-3. The stability of Lanthanide Oxide-modified
catalysts supports is further demonstrated in later examples.
EXAMPLE 2
Preparation of Catalyst For Use In 5.1-cm Diameter Reactor
3,050-g samples of various microspheroidal alumina supports
modified by incorporating therein various amounts of Lanthanide
Oxide prior to calcination were placed in heavy-gauge plastic bags.
An aqueous solution of 773 g copper(II) chloride dihydrate, 407 g
potassium chloride and 1455 g water was then added to each of the
alumina samples in the plastic bag. Sufficient solution was present
to moisten all of the alumina. Each preparation was thoroughly
mixed by hand kneading, placed in a glass dish and dried overnight
at 150.degree. C. When the alumina support had a surface area in
the range from about 150 to 200 m.sup.2 /g, target loadings of
catalysts prepared therewith were 15.0 and 10.0 percent copper
chloride and potassium chloride, respectively, calculated as the
weights of the anhydrous metal chlorides based on the weight of the
finished catalyst. Salt loadings were adjusted dependent on the
surface area of the support. Thus, for instance, with alumina
supports having surface areas in the range from about 20 to about
100 m.sup.2 /g, significantly lower loadings, e.g., about 9 percent
CuCl.sub.2, 3.7 to 6.5 percent KCl, and, optionally, 4.1 to 6.5
percent MgCl.sub.2, were successfully used.
The actual catalyst compositions produced, the conditions used in
the runs in which they were tested as well as the results obtained
in these tests are shown in Table I, Runs I-4, I-5 and I-6. A
description of the test reactor is given in Example 4 below.
EXAMPLE 3
Catalyst Life Test In 15.2-cm Fluidized Bed Oxychlorination
Reactor
The selected catalyst charge is listed in Table I, I-1, I-2 or I-3
and described in Example I was used in the quantity described in
Table II and tested in the reactor identified in Table II.
The selected charge was loaded into a pressurizable reactor
fabricated from 15.2-cm diameter Inconel 600 nickel alloy pipe 396
cm in length. Welded into the top and bottom of this reactor
section were four 1.9-cm diameter tubes running the length of the
section and standing out 2.5 cm from the wall. "Dowtherm A" heat
transfer medium was circulated through these tubes for cooling. A
distributor was flanged to the bottom of the reactor section and an
enlargement section to the top. The enlargement tapered from the
15.2-cm pipe section through a 60-degree cone into a cylinder 40.6
cm in diameter and 61.0 cm high. The effluent line of this reactor
was equipped with a cyclone with a catalyst return leg, a fines
filter and a pressure control valve. Thermowells were welded into
the side of the reactor tube at various levels. The reactor and
accessory equipment were electrically heated and insulated.
The quantities and rates of catalyst charged and feeds introduced
into the 15.2 cm diameter reactor, as well as the average operating
conditions, are shown under Run No. II-3 in Table II below.
Catalyst samples were removed periodically through a valve without
shutdown.
EXAMPLE 4
Catalyst Life Test in 5.1-cm Fluidized-Bed Oxychlorination
Reactor
A pressurizable oxychlorination reactor fabricated from 5.1-cm
diameter Inconel 600 nickel alloy pipe 396 cm in length was used in
measuring the life of various other catalysts in this example.
Welded around the reactor tube was a pressurized 10.2-cm pipe
jacket connected into a thermosyphon filled with "Dowtherm A" heat
transfer medium for cooling. The reactor was equipped with a
distributor at the bottom and an enlargement at the top. The
enlargement was 15.2 cm in diameter and 122 cm long, tapering
downward to its flange connection with the 5.1-cm reactor tube. The
effluent line was equipped with a cyclone, fines pot, fines filter
and pressure control valve. A 0.6-cm Inconel tube, extending the
length of the reactor tube, contained a sliding thermocouple. The
reactor, effluent line and accessory equipment were electrically
heated and insulated.
Various microspheroidal catalysts (see Table I, Runs I-4, I-5, I-6)
in the quantity prepared in Example 2 were loaded into the reactor.
The reactor was periodically shut down and depressurized for
removal of catalyst samples for surface area analysis. The
quantities of catalyst charged, rates of feed introduced into the
5.1 cm reactor, as well as the operating conditions are shown under
Run No. II-2 in Table II below.
As the reaction aging data in Table I show, the catalyst
composition tested in Run I-4, prepared from unmodified high purity
alumina, suffered very major reductions in surface area, i.e., this
catalyst showed itself to be thermally quite unstable under the
conditions of these tests. This is in sharp contrast to the novel
catalyst compositions using Lanthanide Oxide-modified catalyst
supports described in Example 2 and tested in Run I-5 and I-6.
A Lanthanide Oxide-stabilized catalyst life test was also completed
using a 3.8-cm diameter reactor, Run No. I-7, Table I. The reactor
is fully described in Example 8 with run conditions described in
Table II, run No. II-3. Comparative tests have shown that similar
performance is obtained with the 3.8-cm, 5.1-cm and 15.2-cm
diameter reactors. Results obtained in Run I-7 again confirm the
stability of Lanthanide Oxide-stabilized catalysts. One should note
that the tests were conducted in all three reactors under reaction
conditions that were identical or very similar, except that in the
runs conducted in the 3.8 cm reactor (Table II, Run No. II-1) the
catalyst charge was much less and the superficial linear velocity
was only about half that used in the tests conducted in the 5.1 cm
and the 15.2 cm reactors (Table II Runs No. II-2 and II-3).
TABLE I
__________________________________________________________________________
Properties of Supports and Catalysts Before and After Reaction
Aging Lanthanide Catalyst Salt Run Oxide, Initial Loading Area
Weight Surface Area, m.sup.2 /g CuCl.sub.2 KCl MgCl.sub.2 Run Time,
Run Temp., Final Surface No. Support Percent Support Catalyst
Weight Percent Hours .degree.C. of Catalyst, m.sup.2
__________________________________________________________________________
/g Tested in the 15.2-cm diameter reactor I-1 Alumina A 0.0 190 73
15.0 10.0 -- 288 418 9 I-2 Alumina B 0.0 166 72 15.0 10.0 -- 540
418 16 I-3 Alumina E 4.9 (1) 47 27 9.1 4.1 4.1 950 418 26 Tested in
the 5.1-cm diameter reactor I-4 Alumina C 0.0 35 21 8.8 3.7 -- 873
410 14 I-5 Alumina D 4.6 (2) 55 36 9.4 4.4 4.4 394 410 39.sup.a I-6
Alumina E 4.9 (1) 47 28 9.1 4.1 4.1 970 410 31.sup.a Tested in the
3.8-cm diameter reactor I-7 Alumina F 2.5 (3) 92 33 9.0 6.5 6.5 223
411 43.sup.a
__________________________________________________________________________
.sup.a The higher catalyst surface at the end of the runs than
initially is thought to be due to pore opening caused by
dehydration and redistribution of the catalyst salts; some
variability may also be due to nonuniform sampling. (1)
Approximately 58.37% lanthanum oxide, 19.59% neodymium oxide,
14.08% cerium oxide and 7.96% praseodymium oxide (by xray emission
analysis) (2) Essentially pure lanthanum oxide (3) 49.6% lanthanum
oxide, 50.0% cerium oxide and 0.4% neodymium oxide (b xray emission
analysis)
TABLE II ______________________________________ Run Conditions for
Oxychlorination Catalyst Life Studies II-1 II-2 II-3 Reactor
Diameter Run No. 3.8-cm 5.1-cm 15.2-cm
______________________________________ Reaction Parameters Ethylene
Dichloride Feed Catalyst Charge, kg 1.1 4.1 38.6-61.3 Temperature,
.degree.C. 411 410 418 Pressure, atm. 60 60 60 Catalyst Bed Height,
cm 122 259 274-396 Superficial Linear Velocity, 8.5 18.3 18.3
cm/sec Residence Time, seconds 14 14 14-22 HCl/Ethylene Dichloride
Molar 1.2-1.68 1.2-1.68 1.35 Ratio HCl/Oxygen Molar Ratio 0.84-0.95
0.96 0.95 When Ethylene Dichloride Feed Was Replaced by Ethylene:
HCl/Ethylene Molar Ratio -- -- 2.85 HCl/Oxygen Molar Ratio -- --
1.60 ______________________________________
Referring to Table I, Aluminas A, B and C are controls, showing the
losses of surface area obtained when high- and intermediate-surface
area aluminas containing no Lanthanide as a stabilizer were used as
catalyst supports under substantially identical conditions in the
high temperature oxychlorination reaction to make perchloroethylene
and trichloroethylene. Aluminas D and E were experimental
stabilized alumina supports containing 4.6 and 4.9 percent
respectively, of Lanthanide Oxide, and Alumina F was a Lanthanide
Oxide-stabilized support prepared to applicants' order by Akzo
Chemie in the Netherlands, containing 2.5 percent Lanthanide Oxide.
For comparison, the initial surface areas of the catalyst
compositions based on Aluminas D, E and F were of approximately the
same magnitude as that of the catalyst composition based on Alumina
C (control). The results in Table I show a very large degree of
surface area shrinkage in the case of catalysts made with Aluminas
A, B and C (Runs I-1, I-2, and I-4), as opposed to virtually no
significant shrinkage in the case of catalysts made with the
Lanthanide Oxide-stabilized Aluminas D, E and F (Runs I-3, I-5, I-6
and I-7) when used in oxychlorination runs from about 400 to 1000
hours in duration under similar conditions.
The amount of Lanthanide Oxide, if any, incorporated in each
alumina support tested is shown in Table I. The Lanthanide Oxide
employed in the preparation of Alumina D consisted essentially of
pure lanthanum oxide. As determined by x-ray emission analysis, the
Lanthanide Oxide employed in the preparation of Alumina F consisted
of 49.6 weight percent lanthanum oxide, 50.0 percent cerium oxide
and 0.4 percent neodymium oxide.
The Lanthanide oxide employed in the preparation of Alumina E
contained a major proportion of lanthanum oxide and minor
proportions of oxides of praseodymium, neodymium as well as cerium.
More specifically, its use resulted in a modified alumina support
in which the 4.9 weight percent Lanthanide Oxides (Re.sub.2
O.sub.3) were distributed as follows as determined by X-ray
emission analysis:
______________________________________ Lanthanide Oxide In Alumina
Support Weight Percent ______________________________________
La.sub.2 O.sub.3 2.86 CeO.sub.2 0.69 Pr.sub.6 O.sub.11 0.39
Nd.sub.2 O.sub.3 0.96 Total 4.90
______________________________________
As can be seen from Table I, the catalyst compositions based on the
novel Lanthanide Oxide-modified aluminas (Runs I-3, I-5, I-6 and
I-7) exhibited excellent stability of surface area.
STABILITY AND ATTRITION TESTS
EXAMPLE 5
Thermal Stability Tests For Catalyst Support
A 20.0-g sample of commercial "Catapal SB", an unactivated
microspheroidal, high-purity, Boehmite alumina support manufactured
by Continental Oil Company, was weighed into a 100-ml Coors AD-998
alumina crucible. In a 50-ml beaker 1.78 g NdCl.sub.3.6H.sub.2 O
and 11 ml water were mixed to form a solution. The solution was
poured into the crucible with the alumina and mixed thoroughly. The
water adsorption capability of the alumina was 0.59 ml of water per
gram. The above solution was just enough to bring the mixture to
the point of incipient wetness. The resulting dough-like mixture
was dried for two hours at 125.degree. C. The amount of Lanthanide
compound was calculated to produce the desired percentage of
Lanthanide Oxide based on the ignited anhydrous weight of the
"Catapal" support. By preliminary test it was determined that the
"Catapal" alumina support as received lost 30 percent of its weight
on calcination at 1200.degree. C.
The same "Catapal SB" alumina support was similarly treated with
various concentrations of other Lanthanide metal salts, namely
yttrium, lanthanum, cerium, praseodymium and with a commercial
mixture comprising principally lanthanum accompanied by smaller
amounts of neodymium, praseodymium, and cerium. To screen
stabilization effects more efficiently over a short period of time,
dried samples of the Lanthanide-treated alumina were heated in a
Lindbergh high-temperature oven for three hours at 1200.degree. C.,
converting all Lanthanide compounds to the oxides and integrally
incorporating them in the alumina support. Single-point B.E.T.
(Brunauer, Emmett and Teller) Theory surface areas of the various
resulting Lanthanide Oxide-containing supports were measured. The
results of these thermal tests are shown in Table III.
Table III shows that measurable stabilization began with only 0.25
percent La.sub.2 O.sub.3 (Sample 10) in the catalyst support and,
as compared with the control, began to assume major and increasing
importance when present in the 0.5 to 6 percent range.
Concentrations between about 0.5 and about 3 percent of Lanthanide
Oxide are preferred, as the incremental benefit obtained at higher
concentrations is usually small. Results in Table III further show
that Y.sub.2 O.sub.3 also stabilized the support but not as well as
the other Lanthanides used, namely, lanthanum, neodymium,
praseodymium, and a commercial mixture comprising all three.
However, contrary to the action of all the other Lanthanide oxides
tested, cerium surprisingly showed itself to be detrimental in that
it actually increased the loss of surface area as compared with the
control, rather than decreasing it. Lanthanum, praseodymium and
neodymium oxides, mixed Lanthanide Oxides containing two or more of
these three Lanthanides, as well as a mixed Lanthanide Oxides
containing a moderate to low amount of cerium oxide all were very
effective in stabilizing the support, but the use of lanthanum
oxide is preferred.
TABLE III ______________________________________ Thermal
Stabilization of an Alumina Support by Various "Lanthanide Oxides"
Heated at 1200.degree. C. for Three Hours "Lanthanide Oxide" (as
"Lanthanide" sesquioxide Surface Sample Salt Used As except as
noted) Area No. Modifier Wt %.sup.a m.sup.2 /g
______________________________________ 1 (Control) None 0 6.0 2
NdCl.sub.3 5.6 38.7 3 NdCl.sub.3 2.9 35.0 4 YCl.sub.3 5.6 19.2 5
LaCl.sub.3 5.6 42.0 6 Ce(NO.sub.3).sub.3 5.6.sup.b 4.4 7 PrCl.sub.3
5.6.sup.c 35.4 8 "MolyCorp 5240".sup.d 5.6 41.0 9 "MolyCorp
5240".sup.d 2.7 45.0 10 La(NO.sub.3).sub.3 0.25 9.5 11
La(NO.sub.3).sub.3 0.5 13.3 12 La(NO.sub.3).sub.3 1.00 25.9 13
La(NO.sub.3).sub.3 2.50 39. 14 La(NO.sub.3).sub.3 4.3 39.0
______________________________________ .sup.a Calculated assuming a
30 weight percent loss on ignition, the amount experimentally
determined for the support at 1200.degree. C. .sup.b Calculated as
cerium oxide, CeO.sub. 2 ; not as sesquioxide .sup.c Calculated as
praseodymium oxide, Pr.sub.6 O.sub.11 ; not as sesquioxide .sup.d
Mixture of Lanthanide chlorides; (46% Lanthanide Oxide equivalent)
described as follows: La.sub.2 O.sub.3 28.0% CeO.sub.2 4.5%
Pr.sub.6 O.sub.11 3.5% Nd.sub.2 O.sub.3 10.0%
EXAMPLE 6
Comparative Attrition Test
Pure spray-dried alumina, silica-stabilized alumina and Lanthanide
Oxide-stabilized alumina supports were compared in terms of their
respective attrition resistances, the results being shown in Table
IV below. The stabilized supports were prepared using spray-dried
alumina-base materials and alumina-base materials that were
intrinsically modified with either silica or a Lanthanide Oxide by
impregnation and calcining. The method of preparing such
silica-modified alumina materials is described in copending
application Ser. No. 07/451,303 filed Dec. 15, 1989 while
preparation of Lanthanide Oxide-modified aluminas is described in
the present specification, notably in Example 5 hereinabove. As an
example, the Lanthanide Oxide used in making stabilized alumina
supports, IV-13, IV-14, IV-17 and IV-18, Table IV, was a mixture
having the following composition: La.sub.2 O.sub.3, 60%; CeO.sub.2,
10%; Pr.sub.6 O.sub.11, 7.5%; and Nd.sub.2 O.sub.3, 22.5%. It was
included in the alumina in a concentration of 4% based on the total
weight of the support, the other 96% being essentially pure
alumina. The other Lanthanide-stabilized supports, IV-9, IV-10, IV-
11, IV-15 and IV-16 were prepared using a similar Lanthanide Oxide
mixture or one higher in lanthanum oxide.
The attrition test procedure used was based on the procedure
described in the article by W. L. Forsythe, Jr. and W. F. Hertwig
"Attrition Characteristics of Fluid Cracking Catalysts. Laboratory
Studies," Industrial and Engineering Chemistry, 1200-6, June
1949.
The Lanthanide Oxide-stabilized intermediate-surface area aluminas
No. IV-9 through IV-18 have been found to exhibit very low
attrition in these attrition tests. This contrasts with the very
high degree of attrition obtained with the support used in the best
silica-stabilized aluminas IV-6, IV-7 and IV-8. While the
unmodified aluminas show somewhat better attrition resistance than
the silica-modified aluminas, the latter do have the advantage of
being substantially more thermally stable in the oxychlorination
reactor than the unmodified aluminas. But the Lanthanide-modified
aluminas are, with the exception of IV-9, surprisingly superior to
all the other compositions of both of the other types not only in
terms of thermal stability but also in terms of attrition
resistance. As regards support IV-9, it may be said that this was
obtained in the first experimental preparation of this material and
is not believed to be properly representative. All subsequent
preparations of this material have consistently produced supports
with much lower attrition indices, i.e., much higher attrition
resistance, as shown by supports IV-10 through IV-18.
TABLE IV ______________________________________ ATTRITION TESTS
Sample Surface Kind of Stabi- Attr. No. Area Stabilizer lizer %
Index.sup.a ______________________________________ Alumina supports
IV-1 190 none -- 26.3 IV-2 196 none -- 35.5 IV-3 34.4 none -- 29.4
IV-4 34.5 none -- 25.4 IV-5 36.2 none -- 15.7 IV-6 34.7 SiO2 1.5
31.7 IV-7 54 SiO2 1.6 32.5 IV-8 55 SiO2 1.5 34.5 IV-9 55 Lanthanide
Oxide 4.6 17.1 IV-10 47 Lanthanide Oxide 4.9 3.8 IV-11 52
Lanthanide Oxide 4.6 4.6 IV-12 78 Lanthanide Oxide 4.6 7.2 IV-13 69
Lanthanide Oxide 4.0 7.2 IV-14 58 Lanthanide Oxide 4.0 3.1 IV-15 60
Lanthanide Oxide 4.6 0.9 IV-16 47.8 Lanthanide Oxide 4.6 7.0 IV-17
43.9 Lanthanide Oxide 4.0 1.5 IV-18 44.9 Lanthanide Oxide 4.0 0.3
______________________________________ .sup.a Standard Oil of
Indiana Procedure (Forsythe and Hertwig)
EFFECT OF SURFACE AREA ON CATALYST PERFORMANCE
EXAMPLE 7
Preparation of Catalyst For Use In 3.8-cm Diameter Reactor
An aqueous solution of 129 g of cupric chloride dihydrate, 156 g of
magnesium chloride hexahydrate and 73.1 g of potassium chloride in
238 g of water was prepared and added to Alumina F described in
Table I above, a heavy plastic bag containing 877 g of Alumina F
described in Table I above, a Lanthanide oxide-stabilized alumina
support composed of 2.5 percent Lanthanide Oxide and about 97.5
percent alumina, and having a surface area of 92 m.sup.2 /g.
The constituents were kneaded to a uniform color and consistency in
the closed bag. Sufficient solution was present to create the
consistency of dough. The uniform mixture was placed in a glass
dish in an oven at 150.degree. C. and dried overnight. The target
composition for this catalyst, designated catalyst "I-7" in Table
I, was copper(II) chloride, 9.0%; potassium chloride, 6.5%; and
magnesium chloride, 6.5%; all calculated on the basis of the
weights of anhydrous metal chloride and the alumina support.
EXAMPLE 8
Catalyst Performance Test in the 3.8-cm Diameter Fluidized-Bed
Oxychlorination Reactor
The selected microspheroidal catalyst charge (catalyst I-7, Table
I), was loaded into a pressurizable reactor constructed from 3.8-cm
diameter Inconel 600 nickel alloy pipe 122 cm in length. An
enlargement 15.2 cm in diameter and 25.4 cm in length was welded to
the top of the 122-cm reaction tube. Cooling for removal of heat of
reaction was provided by a 0.6-cm diameter tube passing through the
head of the reactor and extending to within 2.5 cm of the bottom
feed distributor. Inside the 0.6-cm diameter tube was placed a
0.3-cm diameter tube through which cooling air was passed and
allowed to escape through the annulus between the outer and inner
tubes. To the head of the reactor was attached a cyclone, fines
filter and pressure control valve. A 0.6-cm diameter Inconel tube
extending the length of the enlargement and reaction tube contained
a sliding thermocouple. The reactor, enlargement, cyclone, fines
filter and pressure control valve were electrically heated and
insulated. The reactor was shut down and depressurized for adding
or removing catalyst. Catalyst charges and feeds were introduced in
the quantities and rates prescribed in Table II above.
It is believed that intermediate-surface-area supports at least
initially have sufficient binding sites to retain the catalytic
salts at a level sufficient for good performance and that reactor
corrosion is related to the loss of catalyst salts from the
catalyst as surface area is lost in the course of the
oxychlorination process. Because of this, the maintenance of
surface area of intermediate-surface area supports by means of
inclusion of a Lanthanide Oxide in the support in accordance with
this invention will make a particularly valuable contribution to
significantly reduced reactor corrosion and overall process economy
over the long term.
Some of the catalysts tested above were prepared using alumina
supports possessing an initial surface area in excess of 160
m.sup.2 /g while others were prepared using alumina supports
possessing an initial surface area well below 100 m.sup.2 /g, see
Table I. A similar beneficial effect of Lanthanide incorporation on
the thermochemical stability of the catalyst compositions in
high-temperature oxychlorination or calcination processes was
qualitatively demonstrated in every test largely independent of the
support surface area. However the use of a Lanthanide
Oxide-modified support having an initial surface area below 100
m.sup.2 /g, i.e., 20 to 80 m.sup.2 /g, or more particularly from 35
to about 60 m.sup.2 /g, is preferred because of the favorable
effect that support surface areas in this intermediate range exert
on maintaining good HCl conversion while simultaneously minimizing
reactor metal corrosion. Results in Table V show the advantage of
using a catalyst based on a Lanthanide Oxide-modified alumina
support having a surface area within the preferred range of 35 to
about 60 m.sup.2 /g. Catalysts using Alumina E (Table I) having a
surface area of 47 m.sup.2 /g and Alumina F having a surface area
of 92 m.sup.2 /g (Table I) were tested in a 3.8-cm diameter reactor
under conditions as described in Table II.
The catalyst based on Alumina E, which contained 4.9 percent
Lanthanide Oxide, produced a significantly improved HCl conversion
of 91 percent versus 76.9 percent for the catalyst based on Alumina
F, which had a substantially higher initial surface area and
contained 2.5 percent of Lanthanide Oxide. The catalyst efficiency
of the catalyst based on Alumina E also is very significantly
better than that of the catalyst based on Alumina F. The results
are shown in Table V.
TABLE V ______________________________________ Effect of Catalyst
Support Surface Area on Performance Pressure Reactor (3.8 cm I.D.)
HCl/EDC = 1.2, HCl/Oxygen = 0.95 Catalyst Based on: Performance:
Alumina E Alumina F ______________________________________ Support
Surface Area, 47 92 m.sup.2 /g Temperature, .degree.C. 410 411
Pressure, atm. 4.1 4.1 Bed Height, cm 114 114 S.L.V.d, cm/sec.sup.a
8.5 8.5 Residence time, sec 13.3 13 Catalyst Performance HCl
Conversion, % 91.1 76.9 Burning, % 9.1 10.1 PCE1 + TCE Selectivity,
% 69.6 68.6 Efficiency.sup.b 151.6 135.4
______________________________________ .sup.a Superficial Linear
Velocity .sup.b Efficiency = HCl conversion + (Perc + TCE)
Selectivity - Burning (carbon oxides), all values as percent.
USE OF MAGNESIUM CHLORIDE
According to yet another and particularly preferred refinement of
the invention an improved catalyst of the general type described
above is provided which is especially effective in producing a
relatively high proportion of either perchloroethylene or
trichloroethylene as a matter of choice, with low burning losses
and with accompanying increases in the total efficiency of the
reaction under the conditions best suited for producing either
product.
The process of making perchloroethylene and trichloroethylene by
catalytic oxychlorination of C.sub.2 Hydrocarbons is an especially
complex one. In addition to the requirement for a catalyst and for
reaction conditions favoring chlorination of the organic feed at a
rapid rate, the chlorinated intermediates produced must be
dehydrochlorinated at a rapid rate to allow further chlorination.
With all of this, different catalysts as well as different reaction
conditions are usually required depending on whether the production
of perchloroethylene or of trichloroethylene is to be optimized.
Processes for oxychlorinating C.sub.2 Hydrocarbons commonly destroy
a substantial though variable proportion of the organic feed
through its conversion to carbon oxides. Trichloroethylene
production is especially sensitive to high burning rates and
requires care in the choice of catalyst and conditions.
In searching for compounds that would stabilize alumina supports
against loss of surface area in the high-temperature environment of
the oxychlorination reaction used to make perchloroethylene and
trichloroethylene, it has now been unexpectedly found as part of
this investigation that addition of a proper proportion of
magnesium chloride, or other magnesium compound such as magnesium
nitrate or magnesium acetate, to a catalyst composition possessing
the characteristics described earlier herein gives improved
performance in the form of reduced burning and usually also
produces other improvements in terms of increased hydrogen chloride
or chlorine conversion and higher selectivity to perchloroethylene
and trichloroethylene. The improvement in performance has been
found to be especially marked with feed ratios appropriate for the
production of trichloroethylene.
The catalyst according to this embodiment of the invention is
composed of copper(II) chloride, potassium chloride and magnesium
chloride on supports consisting essentially of at least 90% alumina
and at least 0.25 percent, and preferably 0.5 to 10 percent, of a
Lanthanide Oxide. As described earlier herein, the weight ratio of
potassium chloride to magnesium chloride is in the range from 0.5 1
to 3.0:1 in its preferred embodiment and is most preferably within
the range of to 0.5:1 to 2.0:1. The salt ratio chosen is dependent
on the ratio of perchloroethylene and trichloroethylene product
desired. This salt ratio does not vary significantly with the
surface area of the support.
Catalysts based on Lanthanide oxide-stabilized Alumina D, Table I,
were prepared either with magnesium chloride (catalyst "G", Table
VI), or without magnesium chloride (catalyst "H", Table VI). To
further demonstrate the advantages of using magnesium chloride,
similar catalysts, with and without magnesium chloride, "I and J"
respectively in Table VI, were prepared using a silica-stabilized
alumina support containing 1.6 percent silica and having a surface
area of 35 m.sup.2 /g.
TABLE VI ______________________________________ Catalyst
Compositions Salt Loading, Weight Percent Catalyst Support
Stabilizer, % CuCl2 KCl MgCl2
______________________________________ G Alumina D Lanthanide
Oxide, 9.42 4.42 4.42 4.6% H Alumina D Lanthanide Oxide, 9.42 4.42
-- 4.6% I Silica, 1.6% 8.65 3.65 3.65 J Silica, 1.6% 8.65 3.65 --
______________________________________
The following examples illustrates the effectiveness of this kind
of oxychlorination catalyst when using ethylene dichloride as the
organic feed in the production of perchloroethylene and
trichloroethylene. However, the improvement is just as significant
when ethane, ethylene or a partially chlorinated derivative thereof
is used as feed.
As stated earlier, further improvement in catalyst performance is
obtained when magnesium is included in the CuCl.sub.2 /KCl catalyst
composition used where making perchloroethylene and
trichloroethylene by oxychlorination of hydrocarbons. In testing
such catalyst compositions, oxychlorination runs were conducted
using the 3.8-cm diameter pressurized fluidized-bed reactor
described earlier in the example. The results shown in Tables VII
and VIII point up the advantages obtained when the magnesium
chloride-containing catalysts G and I, Table VI, were used. The use
of these MgCl.sub.2 -containing catalysts produced significant
increases in HCl conversion, efficiency and selectivity as well as
a significant reduction in burning of feed as compared with the
results obtained when the catalysts made without any MgCl.sub.2
addition were used.
TABLE VII ______________________________________ Comparison of
Catalysts G and H In 3.8-cm Reactor Tests (Lanthanide
Oxide-Stabilized Alumina) Catalyst G H
______________________________________ MgCl.sub.2 4.42% None Feed
Ratio (Molar) HCl/EDC 1.20 1.20 HCl/Oxygen 0.95 0.95 Catalyst
Performance: HCl Conversion, % 92.7 83.7 Burning, % 10.0 11.7 PCE +
TCE Selectivity 68.8 65.0 Efficiency.sup.a 151.5 137.0
______________________________________ .sup.a Efficiency = HCl
Conversion + (Perc + TCE) Selectivity - Burning, all values as
percent
TABLE VIII ______________________________________ Comparison of
Catalysts I and J In 5.1-cm Reactor Tests (Silica-Stabilized
Alumina) Catalyst I J ______________________________________
MgCl.sub.2 3.65% None Feed Ratio: Molar HCl/EDC 1.19 1.21
HCl/Oxygen 0.96 0.95 Catalyst Performance: HCl Conversion, % 78.9
72.7 Burning, % 11.5 15.2 PCE + TCE Selectivity 66.5 67.6
Efficiency.sup.a 133.9 125.1 ______________________________________
.sup.a Efficiency = HCl Conversion + (Perc + TCE) Selectivity -
Burning, all values as percent
While the series of tests summarized in Table VII is not directly
comparable with the series of tests summarized in Table VIII, both
series show the beneficial effect of the presence of magnesium
chloride in the catalyst. A comparison between the two series
points to the fact that catalysts based on Lanthanide
Oxide-stabilized alumina perform substantially better than similar
catalysts based on silica-stabilized alumina.
EFFECT OF SALT RATIOS ON CATALYST PERFORMANCE
EXAMPLE 9
Use of Salt Ratios To Adjust Product Selectivity
Another new and unexpected advantage of the invention is the
ability to provide flexibility in selectively producing either a
high perchloroethylene yield or nearly equal amounts of
perchloroethylene and trichloroethylene from the C.sub.2
Hydrocarbon feed. The desired product split is accomplished by
adjustment of the cupric chloride, potassium chloride and magnesium
chloride salt ratios in the catalyst. Four catalysts were prepared
using Lanthanide Oxide-stabilized Alumina E (see Table I) having a
wide range of weight ratios of cupric chloride to potassium
chloride and of potassium chloride to magnesium chloride, as shown
in Table IX-A. The catalyst formulations were tested in the 3.8-cm
Inconel pressure reactor described in Example 7 with the catalyst
charge and feeds conditions (which were held constant) as described
in Table II. Performance test results are shown in Table IX-B.
Enhanced selectivity to perchloroethylene is achieved by using a
cupric chloride to potassium chloride ratio of 4.0 to 6.0, with a
ratio of about 5.0 being preferred. When using the relatively high
cupric chloride to potassium chloride ratio of 5/1, it is best to
use a low potassium chloride to magnesium chloride ratio in the
range of 0.2 to 0.5, as shown in catalyst composition E-2, in order
to reduce carbon burning losses and maintain high HCl conversions
and good selectivity to perchloroethylene.
When relatively high selectivity to trichloroethylene is desired,
optimum cupric chloride to potassium chloride and potassium
chloride to magnesium chloride ratios are considerably different
from those used for increasing selectivity to perchloroethylene.
Relatively high selectivity to trichloroethylene is obtained using
catalyst formulations containing cupric chloride to potassium
chloride weight ratios of 0.5 to 2.0, with a ratio of 1.0 being
preferred, plus potassium chloride to magnesium chloride weight
ratios of 1.0 to 3.0, with a ratio of 2.0 preferred, as in catalyst
E-4. Catalysts E-1 and E-3 lead to results intermediate to those
obtained with catalysts E-2 and E-4, respectively.
TABLE IX-A ______________________________________ Catalyst
Compositions Catalyst E-1 E-2 E-3 E-4
______________________________________ Salt, Weight % CuCl.sub.2
9.1 8.0 11.2 6.4 KCl 4.1 1.6 3.2 6.4 MgCl.sub.2 4.1 6.4 1.6 3.2
Weight Ratios CuCl.sub.2 /KCl 2.22 5.0 3.5 1.00 KCl/MgCl.sub.2 1.0
0.25 2.0 2.0 CuCl.sub.2 /KCl + MgCl.sub.2 1.11 1.0 2.33 0.68
______________________________________
TABLE IX-B ______________________________________ Performance of
Catalysts Compositions Tested In The 3.8-cm Reactor Catalyst E-1
E-2 E-3 E-4 ______________________________________ Feed ratios,
molar HCl/Ethylene dichloride 1.2 1.2 1.2 1.2 HCl/oxygen 0.84 0.84
0.84 0.84 Catalyst Performance: HCl Conversion, % 92 90 89 90
Burning, % 14 14 17 15 PCE + TCE Selectivity, % 72 72 70 72 PCE/TCE
molar ratio 1.3 2.3 1.8 0.9
______________________________________
In reading this specification and claims, it should always be
understood that all quantities, ratio and percentages of materials
are expressed on a weight basis unless some other basis is
indicated explicitly or implicitly.
It should also be understood that while the foregoing description
of the invention includes preferred embodiments and specific
working examples, variations and modifications of what has been
described may be employed by those skilled in the art without
departing from the scope or spirit of this invention. Such
variations and modifications are to be considered within the scope
of the appended claims.
* * * * *